Ultrasonic devices have been used to determine the level of liquid inside of a container; and one common practice is to measure from the side or bottom of the container with the ultrasonic transducer attached to the exterior surface of the container. If the transducer is above the liquid level, no return signal is generated as the high frequency used readily travels through liquids and solids but not through air or gas. Installation of the ultrasonic transducer on the side of a container is not always convenient because of space limitations due to the necessity of shielding of radioactive material, or overpacks used with toxic liquids, or the presence of insulation. Accordingly, it is one object of the present invention to provide an ultrasonic detector which can be used inside of a container.
One prior art device for measuring liquid level within a container by ultrasonic means is described in U.S. Pat. No. 2,960,678 which issued on Nov. 15, 1960 to R. B. Beard, et al. In this device, a transmitter and a receiver are located in the top of a container spaced apart from each other above the surface of a liquid in the container. An ultrasonic wave from the transmitter is reflected off the surface of the liquid within the container and is measured for its attenuation by the receiver, the attenuation being proportional to the level of the liquid within the container. However, this device requires separate receivers and transmitters and relies upon the accuracy of the attenuation measurement. Accordingly, it is one object of the present invention to provide a simple, compact detector that can be positioned within a container and that is not dependent upon container geometry.
Another possible arrangement would be to position an ultrasonic transducer within a container such as a drum and when the level of the liquid reaches the transducer, the ultrasonic wave path would be completed through the liquid but if the bottom of the drum or container were not uniform, the reflection of the wave may vary in its direction and intensity and thus, not provide a reliable return signal. Accordingly, it is another object of the present invention to provide a liquid level detector which may be positioned above a liquid without being dependent upon the orientation of the detector or the distance from the liquid surface to the bottom of the container.
These and other objects are accomplished by the invention which is described below: